Cytokines are soluble protein mediators of immune function that are pivotal to a balanced innate or cell-mediated immune response. Since cytokine levels can be indicative of disease progression and/or resolution, and in a growing number of situations cytokines are being evaluated as therapeutics, there is a common need in both basic research and the health care industry to purify and/or measure key cytokines rapidly with accuracy, precision, and sensitivity, but at a low cost. Our long term goal is the replacement of antibodies in cytokine purification and immunoassays with cytokine binding proteins from microbial pathogens, which will be easier to manipulate for various applications and whose production by recombinant DNA technology should allow significant reductions in cost. Most importantly, the assays based on these cytokine binding proteins will be designed for rapid determination of cytokine levels which will be important in the diagnosis and/or monitoring of disease. To validate this approach we will study an IFN-gamma binding protein encoded by a murine poxvirus ectromelia. This protein is one of six known poxvirus cytokine binding proteins, and has the unique property of binding with high affinity both mouse and human IFN-gamma. PROPOSED COMMERCIAL APPLICATION: Virus cytokine binding proteins could be used to purify or to measure rapidly the therapeutically important cytokines with accuracy, precision and sensitivity, but at low cost.